German published patent application (OS) No. 2 124 024 shows a system for regulation or control of shift members of an automatic stepwise transmission of a motor vehicle in which a friction clutch between motor and the portion of the transmission that turns with the vehicle wheels has its engagement controlled with reference to a predetermined change of motor speed with respect to time. This predetermined amount of motor speed change is determined as a quantity that depends on the motor speed value, the motor torque, the direction of shift, the selected gear, the transmission oil temperature and the loading condition of the vehicle.
The value of permissible jolt and the actual value of jolt effect thus calculated by the time derivative of motor speed are supplied to a control circuit the output amplifier of which drives a mechanical control of a pressure controller for actuation of a friction clutch. The peak values of torque and of the oil pressure in the pressure control that occur during the shifting operation are diminished by the provision of delay devices, for example RC circuits in the electronic equipment or oil nozzles in the hydraulic equipment. A disadvantage of this known system is that the actual amount of jolt effect is only imperfectly determined, and the jolt that takes place after the engagement of the friction plates of the clutch, that is caused by the stiffness of the mechanical drive connection to the wheels, is not taken account of.
It is an object of the present invention to provide a more effective calculation of the potential jolt effect, so that the proper time for the engagement of a friction clutch in automatic or semiautomatic gear shifting can be more effectively determined without producing jolts not taken account of in the determination and without requiring the complication of delay and damping devices for smoothing jolt effects.
Briefly, the actual jolt effect (R.sub.ist) is continuously detected and compared with a maximum permissible value (R.sub.S) by comparing two corresponding electrical signals, and the difference between these two signals is supplied to a control stage that produces a signal corresponding to a first control magnitude having a range of values that can be varied by the difference signal generated by comparing the current motor speed (n.sub.M) and a predetermined speed (n.sub.K), and a second control magnitude is formed by the time rate of change of the motor speed (n.sub.M) which is added to the first control magnitude to produce a sum signal that is applied to the control member of a friction clutch between motor and transmission.
Preferably, the regulation stage operates by calculating the angle (.beta.) which is formed by the relative progress (time-slope) of the motor speed (n.sub.M) and of the transmission input speed (n.sub.G) and this angle is then compared with a maximum permissible value (.beta..sub.s) to provide a difference signal which, as the first control magnitude, is added to the second control magnitude whenever the difference between the motor speed (n.sub.M) and the transmission input speed (n.sub.G) falls below a predetermined value (.DELTA.n).
Preferably, also, the actual jolt (R.sub.ist) at any moment is determined by twice differentiating the transmission input speed (n.sub.G). It is also preferred for the first control magnitude to be set at the value "1" whenever the transmission input speed (n.sub.G) lies below a predetermined value (n.sub.GO). Furthermore, preferably the signs of the first control magnitude, of the second control magnitude and of the maximum permissible angle above mentioned (.beta..sub.S) are reversed when the motor speed (n.sub.M), instead of being greater than the transmission input speed (n.sub.G) is smaller than the latter.
It is finally preferable that whenever the transmission input speed (n.sub.G) is greater than the abovementioned predetermined speed (n.sub.K), the range of the first control value is modified by the difference between motor speed (n.sub.M) and transmission input speed (n.sub.G).
The invention has the advantages that it is possible to control the gear shifting jolt in correspondence with the phases of motor and transmission speed conditions that occur during starting and gear shifting in a motor vehicle. For this purpose, it is necessary to determine merely the parameters motor speed and transmission input speed and then, by the provision beforehand of a few criterion values determining the magnitude of the transmission jolt to be expected, a rapid and at the same time smooth closing of the friction clutch members can be obtained both upon starting up and also in shifting gears of the motor vehicle. By the benefit of the invention, it is furthermore possible to constitute an automated clutching operation in such a way that a certain maximum permissible jolt is not exceeded and the control involved therein can also serve for fulfilling known concepts for automatic shifting of a stepwise transmission. This has the advantage that, for example, in the case of converter-type automatic shifts, the jolt value can be controlled and limited with purely electronic means and the array of damping devices that are necessary by the now conventional hydraulic transmission controls can be dispensed with. The input signal values required for clutching control according to the present invention, namely motor speed and transmission input speed, are already today utilized for determining the proper time for shifting between gears in an automatic transmission, so that no additional tachogenerators or similar transducers are necessary for providing the original input magnitudes for the present invention. The additional expense of incorporating the present invention is accordingly limited to purely electronic components and subassemblies. In contrast to the known hydraulic devices and techniques, the method and apparatus of the present invention is independent of the temperature, which in the case of purely hydraulic or electrohydraulic handling of the jolt problem, produces variations adversely affecting the comfort of the vehicle occupants. In view of the so-called integrated electronic components now widely available in considerable variety at low cost, the necessary cost for incorporating the advantages of the present invention into an automatic transmission control system is to be estimated as relatively small.